This project addresses the overall hypothesis that a specific T cell response of sufficient magnitude directed against tumor associated antigens (TAA) expressed by breast cancers, such as HER2/neu, will inhibit breast cancer progression and metastasis. It has been recently shown that HER2/neu directed immunotherapy can have clinical benefits in patients with breast cancer. Although early attempts to target HER2/neu have focused on generating CD8+ T cell responses, often targeting the HLA A2 restricted cytotoxic T cell epitope E75. We hypothesize that we can augment CD8+ T cell responses to the E75 epitope by immunization with both E75 and class II epitopes contained in the HER2/neu protein. This concept is supported by exciting preliminary data which demonstrate HER2/neu specific class II restricted CD4+ T cell responses in patients using HER2/neu intracellular domain (HER2/neu ICD) protein loaded dendritic cells (DC). Briefly, in a pilot study of patients with metastatic breast cancer, we found that immunization with HER2/neu ICD protein loaded DC led to a significant circulating HER2/neu specific T helper response. Based on our data, we propose to immunize patients with mature DC loaded with both the E75 epitope (Class I) and the HER2/neu ICD protein (Class II) to determine the effect of cognate T help in augmenting immunity to CTL epitopes to HER2/neu. We will determine the impact of repeated immunizations on inducing high frequency CD4+ T helper cell responses. We then propose to optimize HER2/neu loading strategies into DC by generating recombinant HER2/neu expressing adenoviral vectors to modify DC. Finally, we will perform a clinical trial immunizing patients with HER2/neu modified DC. This project proposes to extend our previous work with peptide pulsed DC based immunotherapy, leading to sequential clinical trials to optimize the generation of HER2/neu specific CD8+ cytotoxic and CD4+ T helper cell responses. These clinical trials, focusing on optimizing CD4+ T helper responses to HER2/neu, will form the background to rationally choose HER2/neu specific vaccination strategies in trials designed to demonstrate a clinical benefit of HER2/neu directed immunotherapy. Our specific aims are: Specific Aim 1. Perform a phase I clinical trial of HER2/neu E75 and intracellular domain (ICD) protein pulsed mature dendritic cell immunotherapy. Specific Aim 2. Monitor HER2/eu specific T cell responses using ELISPOT analysis Specific Aim 3. Generate HER2/neu ICD encoding recombinant adenoviral vectors to optimize antigen processing by ubiquinization. Specific Aim 4. Perform a phase I clinical trial of HER2/neu ICD modified dendritic cell immunotherapy.